The fabrication of semiconductor or optoelectronic process releases the exhaust fumes containing harmful gases and particles, such as silicon dioxide particles and arsenic particles. The exhaust fumes are first transferred by a vacuum pump to local scrubber in which the exhaust fumes are disposed of by burning and scrubbing. Such a disposal method as described above is limited in effect in that most of the submicron particles are not effectively washed away, and that most of the particles are discharged into the atmospheric air, thereby resulting in air pollution. The main culprit is that the silicon dioxide particles and the arsenic particles are much smaller than one micron and can not be therefore disposed of effectively by scrubbing. In addition, these particles are apt to deposit in the pipeline of the vacuum pump. It is conceivable that the deposition of the particles will eventually result in obstruction of the pipeline of the vacuum pump. On the other hand, nanotechnology application is the future trend of the high-tech industry. Accordingly, there will be nanoparticle pollution which is resulted from the discharge or loss of the nanoparticles amid the production of the nanomaterials. The unwanted nanoparticles can not be effectively disposed of by means of traditional methods. It is therefore readily apparent that research and development of preventive method and apparatus of the nanoparticle pollution are urgently called for.
Cyclone is generally used under normal pressure to remove particles having an aerodynamic diameter ranging from one to ten or more micron. The conventional cyclone dust collectors are mostly of a tangential flow design, with very few of them being of an axial flow design. As far as the research on the axial flow cyclone is concerned, Liu and Rubow disclosed A NEW AXIAL FLOW CASCADE CYCLONE FOR SIZE CHARACTERIZATION OF AIRBORNE PARTICULATE MATTER (Liu, B. Y. H. and RUBOW, K. L., 1984). In addition, Liu, Pui, and Fissan disclosed a step-by-step axial flow cyclone (AEROSOLS, PP. 115–118, Elsevier, Amsterdam) and the experimental data of the particle collection efficiency and the particle loss of each step, with the flow of each step being 30 standard liters per minute (abbreviated as slpm), and with the cut-off aerodynamic diameters being 12.2; 7.9; 3.6; 2.05; and 1.0 μm. Weiss et al. disclosed two kinds of axial flow cyclones which are adapted to collect the particle sample in a workplace. (Weiss, Z., Martinec, P. and Vitk, J., 1987, Vlastnosti Dulnibo Prachu A Zaklady Protiprasne Techniky, Prague, SNTL). The flows of the two axial flow cyclones are respectively 8 and 50 slpm, whereas the cut-off aerodynamic diameters are respectively 4.8 μm and 3.0 μm. Vaughan made a variety of axial flow cyclones (Vaughan, N. P., 1988, Construction and Testing of An Axial Flow Cyclone Pre-separator, J. AEROSOL SCI., 19 (3): 295–305). As the flows of these axial flow cyclones remain between 1.24 and 3.75 slpm, the cut-off aerodynamic diameters remain in the range of 1.6–6.5 μm. The afore-mentioned researches were conducted under the atmospheric pressure on the efficiency of the cyclone dust collectors. There is a lack of research literature on the efficiency of the cyclone dust collectors under low pressure.